INVESTIGATION OF THE CHARACTERISTICS OF FLOOD INUNDATION BY THE HEAVY RAIN OF TYPHOON NO. 19 IN FIRST YEAR OF REIWA

Abstract

 This report investigates the characteristics of heavy rainfall and flood inundation in the area by Typhoon No. 19 in 2019 by examining the heavy rainfall, flood inundation, and breached rivers in the affected areas. From this study, it is clear that (1) In prefecture-managed rivers, flooding occurred due to insufficient flow capacity in heavy rainfall areas and a decrease in flow capacity with rising water levels in the main river, (2) In nationally managed rivers, the rainwater in the upstream basin flowed downstream, and the water level in the river channel increased in areas with relatively little rainfall with causing levee flooding, (3) Depending on the topographical characteristics, there were two types of floodplains, one that attempted to divert floodwater back into the river channel and the other that acted as a retarding basin, (4) The area where the levee breach occurred in the Kanto region, where most of the land use was a field and where the inundation flows was stored, may have roled as a flood retarding basin.